A Mg2 ion-Ca2 ion-activated actomyosin-like ATPase has been isolated from bovine, cat and rat brain. It can be dissociated into actin-like and myosin-like components on Sephadex G-200 columns or by ultracentrifugation in a continuous sucrose gradient. These are concentrated in the synaptosomal fraction. The broad objectives of this project are to study further the chemistry, distribution, changes with development and aging, immunological properties and function of these proteins in brain. Emphasis will be focused on the proteins isolated from the synaptosomal fraction. The synaptosomal fraction will be further subdivided into vesicular and membraneous fractions and the distributionof the protein will be determined. Antibodies will be prepared against the proteins and will be used in studies to evaluate their effects on the electrophysiological activity of the brain, on the uptake, storage and release of putative transmitter agents by synaptosomal and vesicular fractions. Whether or not a tropomyosin-like system functions in the control of the enzymatic activity of the proteins will be investigated. Amino acid composition will be studied. Whether the myosin-like moiety can be split into heavy and light fractions will also be investigated. Localization of the actin-like protein in brain tissue by arrow-head formation with heavy meromyosin will be attempted.